1. Field of the Invention
The present invention is directed to a method of manufacturing a film-covered article. More specifically, the invention is directed to manufacturing an injection-molded article having a thermoformed decorative film covering in a single molding tool.
2. Description of the Related Arts
It is known to manufacture molded articles by a method called in-mold lamination. The method is described in U.S. Pat. No. 3,668,034 ('034). The '034 patent teaches placing a decorative laminate within a mold and then injection molding a polymeric material behind the laminate. The resin inlet is juxtaposed the laminate backing. The polymeric material heats, softens and finally fuses to the backing on the laminate.
This reference does not disclose forming the film, but illustrated are two relatively simple two-dimensional films. These films are easily positioned within a tool and molded into an article. Larger articles with three-dimensional surfaces are much more difficult to properly align within a tool. They must be precisely trimmed to the desired dimension. Because these articles are three-dimensional, it is difficult to precisely trim the article after it is molded. The films are easily trimmed while they are flat, but it is desirable to leave the films untrimmed to have excess material for the molding operation. The excess material is useful to retain the film during the thermoforming operation to enable the film to stretch over the mandrel. Films are normally trimmed after they have been formed.
U.S. Pat. No. 5,599,608, teaches a method of thermoforming a film on a mandrel and then trimming the film after it is removed from the mandrel. After the film is molded, it is trimmed. Removing the film from the forming mandrel eliminates the hard-point tooling references for the precise trimming location of the film. Because the film is flexible and formed in a three-dimensional shape, locating these areas precisely is difficult and time consuming.
These thermoforming references all relate to a two-step process whereby the film is first formed and trimmed into the rough shape of the final film-covered article and then transferred into an injection-molding machine. These methods suffer from a difficulty of thermoforming and trimming the film into precisely the desired shape needed for the finished article. The films are generally made from thermoplastic material such as ABS, thermoplastic olefin, and polycarbonate. The film is heated to pliability and then formed. After the film is formed it is cooled. This cooling causes the film to shrink. Unfortunately, this shrinkage is not uniform along the film. Because the film has been shaped into a three-dimensional surface by stretching, some areas are thicker than other areas. These thicker areas shrink more than the thinner areas. The result of the shrinkage is that the cooled part is shaped differently than the thermoforming tool and the injection-molding tool. It presently requires a great deal of effort to match the shape of the cooled thermoformed film to the injection mold surface.
Among the problems associated with matching the thermoformed film and the injection mold tool are differences between the film shape and the tool surface are wrinkles and plastic leakage between the tool surface and the decorative film surface. It is desirable to combine the thermoforming and injection molding operation to provide a low-cost and reliably in-mold lamination process. It is also desirable to utilize the injection mold surfaces to shape the film and to retain the film on the mold surface during injection molding to eliminate alignment difficulties.
These and other objects, features, and advantages of the present invention will become more readily apparent when viewed in connection with the accompanying drawings wherein like reference numbers correspond to like components.